[TowerTalk] Takeoff Angles and Non-Reciprocal Propagation

[Dan Zimmerman N3OX]

>Now pick any
>spot on the wall that has been illuminated and shine a light back toward
>the edge .

Imagine a pair of yagis in free space.  What one hears from the other
one depends on their relative orientation, correct?

The pattern of an antenna in free space is an interference pattern...
the radiation from different parts of the antenna interferes to form a
pattern on transmit.  Much of the power transmitted from one antenna
"goes out in random directions" and will not be intercepted by the
receiving antenna.  Yet I doubt you'll tell me that a pair of
identical yagis in free space won't obey reciprocity...

Adding the knife edge makes your antenna's response to incoming
signals from beyond the knife edge rather complicated, but it's still
just big antenna with a pattern formed by interference.  Everywhere
there's a bright spot has high response, everywhere there's a dark
spot is a null.  The earth is just part of your antenna.


I'll revisit this with coffee in the morning or maybe someone else can
chime in about antenna reciprocity itself.  It's too late for me to do
anything but mumble "time reversal symmetry" and go to bed.


73,
Dan